Cementless ankle prostheses for total ankle replacement surgeries are known. For example, the Scandinavian Total Ankle Replacement (S.T.A.R.®) system by Small Bone Innovations, Inc. is a three piece prosthesis including a talar component, mobile bearing and tibial component. Like many known systems, the S.T.A.R.® system relies on relatively large projections to fasten the prosthesis to bone. The S.T.A.R.® system, for example, features a fin on the talar implant that inserts caudally into a cut made in the talar dome, and two barrels oriented in the anterior/posterior direction on the tibial implant that insert into drilled holes in the tibia. Disadvantages of prostheses having relatively large projections include requiring a significant amount of bone removal and compromising blood supply in the bone.
Before an ankle prosthesis can be implanted, preparatory cuts in the talus and tibia must be made to facilitate positioning of the prosthesis. Typically, the preparatory cuts are not precisely complementary to the bone-contacting surfaces of the prosthesis. This imprecision may be due for example to differences in bone density across the section of the bone being cut. Imprecise preparatory cuts can result in imprecise fastening of the prosthesis to bone, leading to subsequent subsidence, loosening, and/or aseptic failure.
Also before implantation, a drilling template is typically placed over the pre-cut bone surface to guide the drilling of fastener holes in the bone surface. The drilling template is then removed, the actual prosthesis is positioned on the bone surface, and fasteners are inserted through the fastener holes of the prosthesis into the bone to fasten the prosthesis. Typically, however, the alignment of the drilling template on the bone is not identical to the alignment of the actual prosthesis on the bone, a difference due for example to the bone-contacting surface of the drilling template not corresponding precisely in profile to the bone-contacting surface of the prosthesis. The resulting misalignment between the drilled holes in the prepared bone surface and the holes in the actual prosthesis positioned on the prepared bone surface can also result in imprecise fastening of the prosthesis to bone. This misalignment can be further exacerbated by imprecise preparatory cuts in the bone as described above.
Cementless prosthetic implants that provide less intrusive but more precise and stable fastening to bone are therefore desired.